Net fluid computing unit for use with central computer

ABSTRACT

A computing unit usable in a system for computing the quantity of fluid A in a mixture of fluids A plus B flowing during selected intervals of time includes: an accumulator for pulses produced by suitable metering means, each pulse representing the flow of a predetermined quantity of a mixture of fluids A plus B (as for example oil and water); the accumulator having an output which represents the total quantity of fluid A plus B flowing during at least one of the intervals; a converter responsive to such pulses repeatedly to digitize an input signal which represents the proportion of fluid A in the mixture, and as a function of pulse reception, there being an output register connected to receive the digitized signal; and an accumulator for the contents of the register to accumulate a digital quantity which represents the net amount of fluid A in the mixture that has flowed from the beginning of that one interval.

United States Patent Holm [ June 27, 1972 [54] NET FLUID COMPUTING UNITFOR USE WITH CENTRAL COMPUTER [72] Inventor:

[52] U.S.C1..... ....340/172.5,235/151.35

[51] Int. Cl. ..G01t 5/00 [58] Field of Search ..340/172.5, 347;235/151.35

[56] Relerences Cited UNlTED STATES PATENTS 3,578,405 5/1971 Woodie..235/l51.35

3,553,444 1/1971 Tong ..235/l5l.35 3,108,929 10/1963 Tolin et a1..235/151.35 3,027,086 3/1962 Hargens et al. .....235/151.35 3,337,8558/1967 Richard et a1. 340/172 5 3,361,897 1/1968 Rush 340/172 53,387,282 6/1968 Vacques 340/172 5 3,412,241 11/1968 Spence et al.....235/151.35 3,430,206 2/ 1969 Emyei et al ..340/ 172.5

P D PULSE ACCUMULATOR 3,449,725 6/ 1969 Eckelkamp et a1. ..340/3473,526,757 9/1970 Rees et a]. ..340/l72.5

Primary Examiner-Paul J. l-lenon Assistant Examiner-Mark Edward NusbaumAttorney-White & l-laefliger ABSTRACT A computing unit usable in asystem for computing the quantity of fluid A in a mixture of fluids Aplus B flowing during selected intervals of time includes: anaccumulator for pulses produced by suitable metering means, each pulserepresenting the flow of a predetermined quantity of a mixture of fluidsA plus B (as for example oil and water); the accumulator having anoutput which represents the total quantity of fluid A plus B flowingduring at least one of the intervals; a converter responsive to suchpulses repeatedly to digitize an input signal which represents theproportion of fluid A in the mixture, and as a function of pulsereception, there being an output register connected to receive thedigitized signal; and an accumulator for the contents of the register toaccumulate a digital quantity which represents the net amount of fluid Ain the mixture that has flowed from the beginning of that one interval.

15 Claims, 6 Drawing Figures ACCUMULATOR SCAN (NET on. To

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- RE6\5TE;R Z gg, OR

I l l d 5, 52 DIGH'AL REFERENCE PD PULSE ACCUMULATOR To scg 140.5.;C//2OO OUTPUT I /v vs 70/? Was Ms E. HOLM NET FLUID COMPUTING UNITFOR-USE WITH CENTRAL COMPUTER BACKGROUND OF THE INVENTION This inventionrelates generally to telemetry and control systems, and moreparticularly concerns the preliminary processing and storage of datagathered from multiple transducers at a location which may be relativelyclose to the transducers, for subsequent transmission to a centralprocessor. The discussion of the concepts and principles of theinvention will for the most part be directed to monitoring anddetermination of total flow of a mixture of fluids as well as net flowof at least one of such liquids, as for example oil and gas.

In oil production on fields which have many leases, payment must be madeto each lessor for the oil or gas taken from his property, necessitatingaccurate measurement of total fluid flow and oil flow, over intervals oftime. Normally, crude oil from each well on a lease in piped to acentral collection point where it is treated to allow the separation ofnatural gas, and the separation of oil and water. This is an initialtreatment, and some water is left in the oil. Treatment may be performedin continuous flow, and in addition by the batch, at intervals, but ineither case total fluid flow (oil and water) from a battery may besensed by a positive displacement (PD) meter, and percent oil is sensedby a basic-sediment-and-water (BS and W) probe.

The output of the PD meter may for example be an electrical pulse of 30to 40 milliseconds duration, the pulse representing a fraction of abarrel of total fluid flow (oil and water). The fraction may containonly one significant digit, so that it is of the type 01, 0.06, 0.003for example. While the output of any one PD meter always represents thesame fraction, the outputs of different PD meters may representdifferent fractions. BS and W probes are of two types, one having ananalog voltage output and the other having a frequency output. In eithercase, the output varies as a function of percent oil in the total fluid(oil and water). The PD meters and BS and W probes, being independentlyoperated devices, have asynchronous outputs, and in actual practice itis possible to transmit such outputs from a large number (say hundreds)of measurement locations or stations to a central computer forcomputation of the net oil flow. For example, the product of the PDmeter pulse (representing total flow at a given instant) and the BS andW probe output (representing the oil fraction in the total flow at agiven instant) is proportional to the net oil flow at that instant,correction by suitable calibration constant yielding net oil flow.However, it is found that the data bandwidth requirements for acomputer-based system becomes very large for the high sampling ratesneeded for accuracy where data from hundreds of stations is sampled,necessitating a large, expensive central computer installation. As oneexample, assuming that in an asynchronous system with PD meter pulsewidth of 30 milliseconds and as many as 32 PD meters per remote terminalunit, and 100 remote terminal units per insulation and an accuracyrequirement of ten bits per PD meter pulse, then the total maximum datarate would be 960,000 bits per second (i.e., 32 X 100 X X 30=960,000).

SUMMARY OF THE INVENTION It is a major object of the invention toprovide a means for overcoming the above problems in a manner resultingin a number of advantages, as outlined below. Basically, the inventioncontemplates the provision of a synchronous system wherein asynchronousdata (as for example representing total flow, and percent oil in theflow) may be acquired in accumulators at each remote terminal unit. Theremote terminal units (RTUs) may then be scanned, synchronously, by acentral digital computer, the bandwidth requirements of datatransmission being very much smaller than for the asynchronous systemdescribed above. For example, if each RTU were scanned once every 10seconds, and there were 100 RTUs each with 32 PD meters and dataaccuracy of 10 bits, then the bit rate would be 4,800 bits per secondsince only 30 samples of a 10 bit number would have to be accumulatedwhich only requires a 15 bit accumulator (i.e., 32 X X l/l0 X 15 4,800).

It is a further object of the invention to provide RTUs especiallyadapted for use in such a synchronous system, each RTU comprising anaccumulator for pulses produced by suitable metering means, each pulserepresenting the flow of a predetermined quantity of a mixture of fluidsA plus B (as for example oil and water), the accumulator having anoutput which at any time represents the total quantity of fluid A plus Bflowing from the beginning of a selected interval of time; a converter(analog to digital, or frequency to digital) responsive to such pulsesto digitize a transducer produced input signal which at any timerepresents the proportion of fluid A in the mixture A plus B flowing atthat time (as for example the percent oil in the oil and water mix),there being an output register connected to receive the digitizedsignal; and an accumulator for the contents of the register toaccumulate a quantity which at any time represents the net amount offluid A in the mixture A plus B that has flowed from the beginning ofthat interval. As mentioned, a computing system may include a number ofsuch computing units (or remote tenninal units, i.e. RTUs),asynchronously acquiring data in the accumulators, the system includinga central computer operatively connected in synchronous scanningrelation with multiple accumulators defined by the RTUs.

Other advantages include: a lower sampling-rate capacity required of thecentral computer input/output bus; fewer priority interrupts required ofthe central computer; smaller core storage for the central computer isneeded since the core need not be sized to accommodate peak possibledata rates; data reliability is greater because data is stored in boththe central computer and the RTUs, with concomitant reduced probabilityof loss of data from any one equipment malfunction; and a conversion tomanual operation in the event of computer malfunction is easier becausethe data is stored in the RTU accumulator.

As will be seen, the invention overcomes disadvantages of prior systemsin that it provides time shareability of the conversion means; itprovides an incremental volume process as respects the flowmeter and mayoperate directly with a positive displacement meter or any other flowmeasuring device which can be caused to produce a pulse representing anincrement of fluid flow (as distinguished from prior devices whereinfrequency operation negates operation with a pulse). Also, the inventionenables direct measurement of total volume and percent thereof of theto-be-measuredconstituent, rather than percentages of wanted andunwanted constituents and then summing them.

It is a further object of the invention to provide a net oil computingsystem which may be time shared with a gas flow computing system, aswill be described.

These and other objects and advantages of the invention, as well as thedetails of illustrative embodiments, will be more fully understood fromthe following description and drawings, in which:

DRAWING DESCRIPTION FIG. 1 is a system block diagram;

FIG. 2 is a block diagram of a remote terminal unit; FIGS. 3 and 4 areelevations showing flow transducers; FIG. 5 is a waveform diagram; and

FIG. 6 is a modified system block diagram.

DETAILED DESCRIPTION Referring first to FIG. 1, a first series of remoteterminal units (RTUs) is indicated at X as connected with a party line Yanother series of RTUs is indicated at X as connected with party line Yand a third series of RTUs X, is connected with party line Y The partylines are also connected with a computer interface unit 10 which isconnected at 11 with the computer 12, the latter being connectable ifdesired to the remote data processing facility 13 via interface 14.Input/output devices 15 and disc file 16 are connected with computer 12;and manual control console 17 is connectedwith the unit 10. It will beunderstood that the computer 12 scans the RTUs (and specifically thedata storage units thereof) on a repetitive basis.

Referring to FIG. 2, each RTU illustrated at X incorporates a firstaccumulator 20 for pulses produced by positive displacement meteringmeans as indicated at 21, the accumulator having an input terminal at22. Each pulse represents the flow of a predetermined quantity of amixture of fluids A plus B, as for example oil and water flowing in line23 from the collection point mentioned above. FIG. 4 shows,schematically, one form of metering means as including a chamber 24connected in series with line 23, and containing a vaned rotor 25 therotation of which is proportional to the flow. A sensor 26, as forexample a magnetic pick-up, produces an output pulse each time the rotorrotates through a predetermined angle, so that flow increments are ineffect counted by the accumulator 20. FIG. 5 shows the occurrence ofpulses at the ends of times z, and 1, theintervals At being variable tocorrespond to variable flow rates. Alternatively, other pulse producingdevices are usable (as for example a turbine meter coupled with acounter, or ionization meters).

The RTUX also incorporates a converter (as for example analog to digitalconverter ,30, or a frequency to digital converter) responsive to eachpulse (or a selected number of pulse s) to digitize a transducerproduced input signal (say at input terminal 31) which at any timerepresents the proportion of fluid A in the mixture A plus B flowing atthat time. For

example, the input signal at terminal 31 may represent the fraction ofoil in the oil and water mix flowing in line 23, there being abasic-sediment-and-water probe or transducer. 32 to produce that signal.One such probe is represented by the capacitor 37 in FIG. 3, connectedin a capacitance bridge 200 as shown, energized at 38. The oil and watermix flows between the capacitor plates and the dielectric strength isthereby varied as a function of the oil fraction, so that the bridgeoutput signal applied to terminal 31 of FIG. 3 varies correspondingly.

Converter 30 in :effect multiplies the inputs at terminals 31 and 27a,to produce a digital output at 41 which represents the net amount offluid A (say oil) in the incremental mixture that has flowed during thevariable pulse interval, say At. That is, a pulse at terminal 27doperates via control 51 to enable the conversion or digitizing, asreferred to. That output at 41 is transmitted. via a suitable gate 42 toan accumulator 43 in which is accumulated a quantity which at any timerepresents the net amount of fluid A in the mixture A plus B that hasflowed during multiple pulse intervals, as for example from thebeginning t,, of the pulse intervals in FIG. 5. Similarly, accumulator20 accumulates a quantity which at any time represents the total amountof fluid in the mix A plus B that has flowed during those same multiplepulse intervals. For example, if each pulse represents 0.01 barrels ofoil and water, and if the input signal at 31- represents 96.2 percentoil, the decimal value 0.00962 barrels of oil wouldbe transmitted at 41;also thedecimal value 0.01 oil and water would be added to accumulator20. Therefore, the accumulators may be synchronously scanned at somerate which may or may not be related to Al, and as described above.

Referring again to the converter, it may advantageously comprise ananalog to digital converter 30 shown in FIG. 2 as including a resistanceladder, represented by digital to analog converter (DAC) 46 havingreference input via switch 73. The converter 30 also has an outputregister 49 receiving input fromterminal 31, as via a comparator 47.having output 50, and a control 51 having output 52. The digital valuestored in the register 49 is transmitted at 54 and 55 via gating 56 tothe DAC to complete the loop.

It will be noted that the same ADC 30 may also be used, on a time sharedbasis, to compute the value of a quantity (AP/T X P) representing totalnet flow Q of gas in a line (as'for example gas separated from the oiland water in the battery referred to above), and in the manner describedin my copending application, REMOTE TERMINAL COMPUTING UNIT FOR USE WITHCENTRAL COMPUTER." For that purpose, there may be input terminal 60 fora signal representing the gas pressure difi'erential AP across anorifice in the gas line; 61 for a signal representing temperature T inthe gas line; and 62 for a signal representing the pressure P in the gasline. In that event, additional elements to enable such computationinclude the sample and hold amplifier 63, square root amplifier 64,vreference supply 65; and accumulator 66 connectable by switch to theoutput-of the register 49. Also, note switch 67 operable between outputs68 and 69 of the elements 63 and 64; switch 101 to control connection ofthe comparator 47 with probe 32; switch 70 to connect the DAC outputalternately to gating 42, to the terminal 71 connected to the comparatorinput, and to the terminal 72 connected to the square root amplifierinput; and switch 73 alternately connectable to terminals 61, 62 and 74(connected to reference supply 75). Control 51 may control switchoperation in various modes.

In the event of such time shared operation, the ADC 30 is operablesuccessively in four modes, the first three of which are described insaid companion application in connection with successive time intervalst t and l The fourth mode would occur during a fourth time interval andbe as described herein for the connections shown in FIG. 2, the control51 operating the appropriate switches for mode control.

Finally, FIG. 6 shows a single ADC having an input terminal 161 forpulses, and another input terminal 162 for input signals representingoil or water fractions in the total flow in different pipe lines 163,164 and 165. PD meters are indicated at 166, 167 and 168 with outputs toaccumulators 169 171. Pulses are transmitted to flip-flops 172 174 toset them for scanning as bya suitable means represented by wiper 175connected to terminal 161. Such operation is possible since the pulsedurations are on the order of 10 30 milliseconds, whereas the conversion(digitizing) rate of the ADC is on the order of a few microseconds. Theflip-flops will not be re-set until scanning is completed, a conditionfavored by the relative pulse duration and conversion times. Terminals178, 179 and 180 (to which oil fraction signals are transmitted bytransducers 181 183) are also scanned as by means represented by wiper184, such scanning being synchronized with scanning of the pulses storedby the corresponding flip-flops. Accordingly, one RTU is able to serve alarge number of total flow and fractional flow sensors or transducers,as described.

Wherever the term fluid is used herein, it includes flowable streamswhether gaseous, liquid or solid (as for example fluid concrete, moltenmetal, etc.

Various of the blocks shown in the figures may be further exemplified byway of example, as follows:

Item

12 A digital computer, as for example Interdata Models II, III and IV,as described in Auerbach Scientific and Control Computer Reports,January 1969.

A suitable interface between the terminal units and computer, forexample including a Channel multiplexer, channel sequence control logicfor input and output data, data formating logic and level bufiering, asis well known in the art, and as may be considered part of computer 12,,as described in said Auerbach publication.

A binary counter as described in Chapter 2 of the text, Digital Countersand Computers by E. Bukstein, published in 1960 by Harcourt, Brace andWorld, New 1 York, New York.

A digital to analog converter of the type described at pp. 1 and 27 ofAnalog/Digital Conversion Handbook" published in 1964 by DigitalEquipment Corporation, Maynard, Massachusetts.

Output register as described at pages 4, 20 and 36 of the abovereferenced "Analog/Digital Conversion Handbook".

I claim:

1. In a system computing the quantity of fluid A in a mixture of fluidsA plus B flowing in a line during selected intervals of time, the systemincluding first means producing pulses each representing the flow of apredetermined quantity of said mixture, a computing unit comprising:

a. a first accumulator electrically connected with said means andaccumulating said pulses, the accumulator producing an output whichrepresents the total quantity of fluid A plus B flowing during at leastone of said intervals,

. a converter electrically connected with the accumulator and respondingto said first means pulses to digitize an input signal which representsthe proportion of fluid A in the mixture A plus B, and as said pulsesare received, and a transducer connected in said line and producing saidinput signal, there being an output register receiving the digitizedsignal, and

Y c. another accumulator electrically connected with said register andaccumulating a digital quantity which represents the net amount of fluidA in the mixture A plus B that has flowed from the beginning of that oneinterval.

2. The unit of claim 1 including an input terminal for said pulses, aninput terminal for said input signal, and means generating said pulsesand said input signal respectively ap plied to said terminals.

3. The unit of claim 2 wherein the converter includes a control circuitresponding to pulse reception to enable said digitizing.

4. The unit of claim 3 wherein the converter comprises an ADC having acomparator connected between the input terminal for the input signal andsaid output register.

5. A computing system including a central computer, and multiplecomputing units as defined in claim 3, and which include multiple firstaccumulators and other accumulators, the computer connected with saidfirst and other multiple accumulators to scan said outputs and saiddigital quantities.

6. A computing unit as defined in claim 1 wherein said first meansinclude multiple positive displacement meters and multiple firstaccumulators receiving and storing pulses from said multiple positivedisplacement meters each pulse representing the flow of a predeterminedquantity of fluid A plus B, the converter successively connected to saidfirst accumulators.

7. The computing units as defined in claim 6 including multipletransducers connected with multiple flow lines to produce multiple ofsaid input signals, and multiple input terminals for said input signal,the converter successively connected to said input terminals insynchronized relation to said successive connection to said firstaccumulators.

8. For use in a computing system, apparatus for computing the quantityof fluid A in a mixture of fluids A plus B flowing in a line during aselected interval of time, the combination comprising:

a. first means for producing pulses each representing the flow of apredetermined quantity of fluid A plus B,

b. accumulator means connected with said first means for accumulatingsaid pulses and having an output which represents the total quantity offluid A plus B flowing from the beginning of said interval,

c. transducer means connected with said line to produce a signal whichat any time represents the proportion of fluid A in the mixture A plus Bflowing at that time, d. converter means connected to be responsive tosaid signal and to said first means pulses to digitize said signal assaid pulses are received, there being an output register connected toreceive the digitized signal, and

e. another accumulator connected with the output of said output registerto accumulate a digital quantity which at any time represents the netamount of fluid A in the mixture A plus B that has flowed from thebeginning of said interval.

9. The combination of claim 8 wherein the converter includes a controlcircuit responding to pulse reception to enable said digitizing.

10. The combination of claim 9 wherein the converter comprises an ADChaving a comparator connected between the input terminal for the inputsignal and said output register.

11. A computing system including a central computer, and multiplecomputing units each as defined by the combination of claim 8, thecomputer connected with the multiple accumulators to scan said outputsand said quantities.

12. The combination of claim 10 wherein the ADC includes a DAC, therebeing an input terminal for a variable T to be connected to the DAC toprovide reference input, another input terminal for a variable AP to beconnected to the ADC operating as a divider during a certain timeinterval to produce an output representative of the quantity AP/T to betransmitted to the DAC, and yet another input terminal for a variable Pto be connected to the DAC operating as a multiplier during another timeinterval to produce an output representative of the quantity AP/T X P,said certain and other time intervals being separate from the timeduring which the converter operates to digitize said transducer producedsignal as a function of pulse reception.

13. The method of computing the quantity of fluid A in a mixture offluids A plus B flowing during selected intervals of time, said methodcomprising the steps of:

a. accumulating pulses each representing the flow of a predeterminedquantity of a mixture of fluids A plus B, and using the pulseaccumulation to produce an out ut representing the total quantity offluid A plus B flowing during at least one of such intervals, andproducing an input signal which represents the proportion of fluid A inthe mixture A plus B,

b. receiving said pulses and said input signal and repeatedly digitizingsaid input signal upon repeated pulse reception, and storing thedigitized input signal, and

c. accumulating the stored digitized input signal to produce a digitalquantity which represents the net amount of fluid A in the mixture Aplus B that has flowed from the beginning of that one interval.

14. The method of claim 13 including the step of generating said pulsesand said input signal.

15. The method that includes performing the computations as defined inclaim 13 at each of a plurality of stations associated with differentmixtures of fluids A plus B, and repeatedly and sequentiallytransmitting to a central computing location said outputs and digitalquantities associated with said stations.

UNITED STATES PATENT OFFICE v CERTIFICATE OF CORRECTION Patent No.3,673,574 Dated June 27, 1972 lnventofls) Wayne E. Holm It is certifiedthat error appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

Column 5, lines 36 and 37; "pulses, an input terminal for said inputsignal, and means generating said pulses and said input signalrespectively apshould read pulses, an input terminal tor said inputsignal, said pulses and said input signal respectively ap- Column 5,line 59; "minals for said input signal, the

converter successively conshould read minals for said input signals, theconverter successively con Signed and sealed this 6th day of February1973.

(SEAL) Attest:

iil)W/\Rl) MJI LIIILIHI-IR JR. ROBERT GOTTSCHALK Attesting OfficerCommissioner of Patents FORM PO-1 1 USCOMM-DC 60376-P69 9 U 5.GOVERNMENT PRINTING OFFICE: I969 O-366334

1. In a system computing the quantity of fluid A in a mixture of fluids A plus B flowing in a line during selected intervals of time, the system including first means producing pulses each representing the flow of a predetermined quantity of said mixture, a computing unit comprising: a. a first accumulator electrically connected with said means and accumulating said pulses, the accumulator producing an output which represents the total quantity of fluid A plus B flowing during at least one of said intervals, b. a converter electrically connected with the accumulator and responding to Said first means pulses to digitize an input signal which represents the proportion of fluid A in the mixture A plus B, and as said pulses are received, and a transducer connected in said line and producing said input signal, there being an output register receiving the digitized signal, and c. another accumulator electrically connected with said register and accumulating a digital quantity which represents the net amount of fluid A in the mixture A plus B that has flowed from the beginning of that one interval.
 2. The unit of claim 1 including an input terminal for said pulses, an input terminal for said input signal, and means generating said pulses and said input signal respectively applied to said terminals.
 3. The unit of claim 2 wherein the converter includes a control circuit responding to pulse reception to enable said digitizing.
 4. The unit of claim 3 wherein the converter comprises an ADC having a comparator connected between the input terminal for the input signal and said output register.
 5. A computing system including a central computer, and multiple computing units as defined in claim 3, and which include multiple first accumulators and other accumulators, the computer connected with said first and other multiple accumulators to scan said outputs and said digital quantities.
 6. A computing unit as defined in claim 1 wherein said first means include multiple positive displacement meters and multiple first accumulators receiving and storing pulses from said multiple positive displacement meters each pulse representing the flow of a predetermined quantity of fluid A plus B, the converter successively connected to said first accumulators.
 7. The computing units as defined in claim 6 including multiple transducers connected with multiple flow lines to produce multiple of said input signals, and multiple input terminals for said input signal, the converter successively connected to said input terminals in synchronized relation to said successive connection to said first accumulators.
 8. For use in a computing system, apparatus for computing the quantity of fluid A in a mixture of fluids A plus B flowing in a line during a selected interval of time, the combination comprising: a. first means for producing pulses each representing the flow of a predetermined quantity of fluid A plus B, b. accumulator means connected with said first means for accumulating said pulses and having an output which represents the total quantity of fluid A plus B flowing from the beginning of said interval, c. transducer means connected with said line to produce a signal which at any time represents the proportion of fluid A in the mixture A plus B flowing at that time, d. converter means connected to be responsive to said signal and to said first means pulses to digitize said signal as said pulses are received, there being an output register connected to receive the digitized signal, and e. another accumulator connected with the output of said output register to accumulate a digital quantity which at any time represents the net amount of fluid A in the mixture A plus B that has flowed from the beginning of said interval.
 9. The combination of claim 8 wherein the converter includes a control circuit responding to pulse reception to enable said digitizing.
 10. The combination of claim 9 wherein the converter comprises an ADC having a comparator connected between the input terminal for the input signal and said output register.
 11. A computing system including a central computer, and multiple computing units each as defined by the combination of claim 8, the computer connected with the multiple accumulators to scan said outputs and said quantities.
 12. The combination of claim 10 wherein the ADC includes a DAC, there being an input terminal for a variable T to be connected to the DAC to provide reference input, another input terminal for a variable Delta P To be connected to the ADC operating as a divider during a certain time interval to produce an output representative of the quantity Delta P/T to be transmitted to the DAC, and yet another input terminal for a variable P to be connected to the DAC operating as a multiplier during another time interval to produce an output representative of the quantity Delta P/T X P, said certain and other time intervals being separate from the time during which the converter operates to digitize said transducer produced signal as a function of pulse reception.
 13. The method of computing the quantity of fluid A in a mixture of fluids A plus B flowing during selected intervals of time, said method comprising the steps of: a. accumulating pulses each representing the flow of a predetermined quantity of a mixture of fluids A plus B, and using the pulse accumulation to produce an output representing the total quantity of fluid A plus B flowing during at least one of such intervals, and producing an input signal which represents the proportion of fluid A in the mixture A plus B, b. receiving said pulses and said input signal and repeatedly digitizing said input signal upon repeated pulse reception, and storing the digitized input signal, and c. accumulating the stored digitized input signal to produce a digital quantity which represents the net amount of fluid A in the mixture A plus B that has flowed from the beginning of that one interval.
 14. The method of claim 13 including the step of generating said pulses and said input signal.
 15. The method that includes performing the computations as defined in claim 13 at each of a plurality of stations associated with different mixtures of fluids A plus B, and repeatedly and sequentially transmitting to a central computing location said outputs and digital quantities associated with said stations. 